Using a spectrodensitometric assay which permits analysis of small quantities of lipid it will now be possible to measure cholesteryl ester synthetase and hydrolase in preparations from one rabbit or 3 rat aortas. We will study esterification in vitro of trans unsaturated fatty acids by preparations from rat and rabbit aorta. We will also study sex differences in cholesteryl esterase activity in rats and rabbits. Another series of studies will investigate the effects of semipurified diets rich in various carbohydrates or proteins on aortic cholesteryl ester in rabbits and rats.